1. Field of the Inventive Concept
The present inventive concept relates to methods for fabricating semiconductor device.
2. Description of the Related Art
As a size of a metal oxide semiconductor (MOS) transistor has been reduced, a length of a gate and a length of a channel in the MOS transistor are also gradually decreasing. Accordingly, various studies have been done to increase capacitance between the gate and the channel and to improve operating characteristics of the MOS transistor.
Metal-oxide-semiconductor (MOS) transistors using a polysilicon gate electrode are widely known. Since polysilicon is capable of withstanding well at a higher temperature than most metals, it may be annealed at a high temperature with a source and drain region. In addition, since polysilicon may reduce implanting of doped atoms into a channel region, a self-aligned source and drain structure may be formed after a gate patterning process.
Polysilicon has higher resistance than most metals, and a polysilicon gate electrode operates at a lower speed than a metal gate electrode. One of the methods for compensating for high resistance of polysilicon is replacing the polysilicon gate electrode with a metal gate electrode using a replacement metal gate (RMG) process. A high-temperature process is performed while polysilicon gates remain on a semiconductor substrate, and the polysilicon gates are removed after performing the high-temperature process to be replaced by metal gates, thereby forming a replacement metal gate (RMG).